The present invention relates to a variable resistor the resistance value of which is variable by rotating a sliding member on a resistor formed on an insulating substrate and capable of being mounted on a surface of a printed circuit substrate and the like, and in particular to a construction of outside electrodes provided on the insulating substrate.
A variable resistor of this type, in which an arched thermet resistor 5 is formed on an upper surface of an insulating substrate 1 and a sliding member (not shown) is rotatably mounted on the insulating substrate 1 so as to slide on the resistor 5, as shown in FIG. 9, has been proposed. The sliding member is rotatably mounted in a central hole 2 of the insulating substrate 1 through an electrode (not shown).
In addition, the resistor 5 is provided with outside electrodes 6 formed of silver-palladium alloy at both ends thereof. These outside electrodes 6 are formed by at first printing silver-palladium alloys 6a, 6b on the one surface and the opposite surface of the insulating substrate 1 and then printing the same silver-palladium alloy 6c on end faces, as shown in FIG. 10. Subsequently, the resistor 5 is printed on the outside electrodes 6.
However, in the above described variable resistor in order to prevent silver from diffusing in the solder and to improve the heat-resisting characteristics of the solder, a silver-palladium alloy is used for the electrodes 6 but this is expensive and a problem occurs in that it is impossible also to surely prevent silver from reaching the solder. In addition, the film-thickness of the silver-palladium alloy 6c provided on the end faces can not but be increased and glass frits are exposed on the surface to spoil the soldering characteristics, whereby a problem occurs also in that a troublesome preliminary soldering is required.